The present invention relates, in general, to manufacturing of semiconductor devices, and more particularly, to slurries used to polish semiconductor wafers.
Polishing of semiconductor wafers was a common technique often used by the semiconductor industry to planarize semiconductor wafers, and to reduce the thickness of semiconductor wafers. Wafer polishing operations generally used an aqueous slurry which typically included fine abrasive particles that were suspended in a strong alkali metal base, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). The base adjusted the slurry's pH value to ensure that the abrasive remained in suspension, to assist in chemical removal of material from the wafer, to maximize removal rate, and to ensure surface smoothness. Although the polishing operations were generally performed in an enclosed polishing apparatus, alkali cations such as sodium ions (Na.sup.+) or potassium ions (K.sup.+) escaped from the slurry. The cations were small mobile ions that contaminated a wafer processing area and the wafers in the area by rapidly diffusing through the wafer processing area, contacting wafers in the area, and diffusing into the wafers. Semiconductor devices produced from the contaminated wafers had numerous defects including high leakage current, surface inversion, low breakdown voltage, and inferior semiconductor device performance.
Accordingly, it is desirable to have a wafer polishing slurry that does not contain highly mobile ions, that does not contaminate the environment of a semiconductor wafer processing area, and that does not cause inferior semiconductor device performance.